[TowerTalk] Shack to service entrance ground

[Jim Brown]

On 8/18/2023 8:05 PM, john at kk9a.com wrote:
> I am wondering why nearly everything is made this way. Is connecting to the
> chassis too costly?

Yes. For 30-40 years, standard practice has been to build boards with 
connectors mounted to the board and shove them into an enclosure with 
holes for connector to fit through. It costs more build so that the 
shield contact makes contact with the enclosure (if it's conductive at 
all).

The problem exists in some products when intended contact with the 
enclosure is insulated by paint. Every Astron PSU I opened around 2010 
had that fault -- the power line green wire was soldered to the mounting 
lug of an old-fashioned terminal strip that was insulated from the 
chassis by paint, AND V-, which was properly floated on the circuit 
board, was, by default bonded to that lug. I'd seen reports that these 
supplies could be unstable; now, I knew why!  I published this on my 
website at that time in this app note, which W4TV, W8JI, and I discussed 
at the time. For the products he sold that needed 12VDC, he urged users 
to run them from a 12V wall wart rather than the DC buss.

http://k9yc.com/PowerSupplyBondingAndAudioDistortion.pdf

And there's ignorance of the issue, in large part due to "Balkanization" 
of electronics education by specialization. So much of the industry is 
dominated by those with digital and computer training; only when Johnson 
and Graham published two important books analyzing microstrip and 
stripline as transmission lines did that classic discipline enter their 
universe. Henry Ott introduced me to "High Speed Digital Design" and 
"High Speed Propagation," sub-titled "A Handbook of Black Magic" and 
"Advanced Black Magic" in a 3-day EMC class I took from him around 2003. 
I may have been the only analog guy in a class of 20-25 engineers, and 
at 62, probably the oldest.

Pro audio is the only part of the industry that I'm aware of that 
cleaned up their act, based on an important EMC papers session at an AES 
convention in Los Angeles in 1994, all of them published in the June '95 
Journal of the Audio Engineering Society. It became the most re-printed 
edition of the Journal, and manufacturers all adopted the practices 
raised by the 6-8 presenters. One of them, an engineer at Rane Corp, a 
manufacturer based in the Pacific Northwest, showed the problem in their 
gear. A few years later they reported that their support calls for hum, 
buzz, and RFI were reduced by a factor of 25 or more after they made 
running production changes throughout their product line. When Neil 
Muncy published his paper on Pin One in 1994, every product on the very 
large exhibition floor had Pin One Problems; ten years later, almost 
none did.

73, Jim K9YC